U.S. Pat. No. 3,369,259 issued Feb. 20, 1968 discloses a flapper valve for a flush tank in which the valve comprises a rubber element arranged to engage the valve seat of a flush tank outlet and wherein the rubber portion of the valve is reinforced by a rigid ring like structure having arms which are pivotally connected to a fixed pivot. The arrangement of this patent is not well adapted to accommodate minor shifting of the flapper valve relative to the outlet seat due to the rigid nature of the reinforcing structure for the flapper valve and the fixed pivotal mounting of the rigid structure.
U.S. Pat. No. 3,707,733 issued Jan. 2, 1973 discloses a flapper flush valve formed of flexible resilient material and which does not include rigid reinforcing elements used in conjunction with the flexible resilient material. Without reinforcement, the valve element of this patent tends to operate in a somewhat erratic fashion on occasions and is not of a particularly durable nature.
U.S. Pat. No. 3,988,785 issued Nov. 2, 1976 is similar to the above mentioned Pat. No. 3,369,259 in that it utilizes rigid elements in conjunction with flexible yieldable means.
U.S. Pat. No. 4,497,076 Sullivan issued Feb. 5, 1985 discloses a flapper valve having pivotally mounted structure which is loosely coupled to a fixed pivot. This loose coupling allows limited shifting of the flapper valve but also lacks the precision of operation which could characterize a more closely controlled valve movement.